Carbon nanostructures have received a great deal of interest since their discovery. It has been suggested that carbon nanostructures may have important applications in electronics, in materials sciences, and in a number of additional fields. As used in this disclosure, a carbon nanostructure comprises a structure formed from chemically bonded carbon atoms, with or without impurities or intentionally added materials incorporated in the carbon structure or adjacent to the carbon structure. Carbon nanostructures include structures in which carbon atoms are arranged in generally a series of interconnected hexagonal rings formed into a tube or other structure. Carbon nanostructures may be single walled or multiple walled nanotubes, nanofibers, nanorope, or nanowire. Single wall nanotubes include a single layer of the hexagonally arranged carbon atoms, while multiple walled nanotubes are made up of an inner layer of carbon atoms and a series of one or more outer layers of hexagonally arranged carbon atom structures.
Despite the interest in carbon nanostructures and the potentially important uses for such structures, the practical application of carbon nanostructures in products has been slowed by the difficulty in manufacturing such structures. Two general types of processes have been employed to produce or isolate carbon nanostructures. One process type uses a plasma arc between carbon electrodes. U.S. Pat. Nos. 5,482,601 and 5,753,088 describe such carbon plasma arc processes for producing carbon nanotubes. Another process type involves simply isolating naturally formed carbon nanotubes from graphite and soot. Such an isolation process or refinement process for carbon nanotubes is described in U.S. Pat. No. 5,560,898.
The prior processes for producing or isolating carbon nanotubes have been found to produce only small quantities of carbon nanotubes of inconsistent quality. The low quality carbon nanotubes produced or isolated by the prior methods commonly included metal or other atoms incorporated in the carbon structure. These impurities incorporated in the walls of the carbon nanotubes may have a negative impact on the qualities and properties of the nanotube and may render it unsuitable for an intended purpose. In particular, prior carbon nanostructure production techniques include no mechanism for preventing hydrogen atoms and other atoms that may be present in the carbon-bearing feed material from being incorporated into the nanocarbon structure. Also, prior carbon nanostructure production techniques tend to allow carbon from the feed material to become incorporated into the carbon nanostructures in an unpredictable fashion outside of the desired interconnected hexagonal ring structure. This inclusion of amorphous carbon in the resulting carbon nanostructure greatly degrades the properties and usefulness of the resulting carbon nanostructure.